Photoconductive recording material comprising a crosslinked binder system

ABSTRACT

A photoconductive recording material described containing a support and a charge generating layer (CGL) in contiguous relationship with a charge transporting layer (CTL) containing a p-charge transporting material (p-CTM), wherein the charge generating layer (CGL) does not contain a charge transporting material but comprises a charge generating material and a binder, wherein the binder is made insoluble in methylene chloride by crosslinking and the binder which is composed essentially of one or more polyepoxy compounds self-crosslinked under the influence of an amine catalyst and/or crosslinked by reaction with at least one primary and/or secondary poly NH-group amine.

DESCRIPTION

1. Field of the Invention

The present invention relates to photosensitive recording materialssuitable for use in electrophotography.

2. Background of the Invention

In electrophotography photoconductive materials are used to form alatent electrostatic charge image that is developable with finelydivided colouring material, called toner.

The developed image can then be permanently affixed to thephotoconductive recording material, e.g. a photoconductive zincoxide-binder layer, or transferred from the photoconductor layer, e.g. aselenium or selenium alloy layer, onto a receptor material, e.g. plainpaper and fixed thereon. In electrophotographic copying and printingsystems with toner transfer to a receptor material the photoconductiverecording material is reusable. In order to permit rapid multipleprinting or copying, a photoconductor layer has to be used that rapidlyloses its charge on photo-exposure and also rapidly regains itsinsulating state after the exposure to receive again a sufficiently highelectrostatic charge for a next image formation. The failure of amaterial to return completely to its relatively insulating state priorto succeeding charging/imaging steps is commonly known in the art as"fatigue".

The fatigue phenomenon has been used as a guide in the selection ofcommercially useful photoconductive materials, since the fatigue of thephotoconductive layer limits the copying rates achievable.

A further important property which determines the suitability of aparticular photoconductive material for electrophotographic copying isits photosensitivity, which must be sufficiently high for use in copyingapparatuses operating with the fairly low intensity light reflected fromthe original. Commercial usefulness also requires that thephotoconductive layer has a spectral sensitivity that matches thespectral intensity distribution of the light source e.g. a laser or alamp. This enables, in the case of a white light source, all the coloursto be reproduced in balance.

Known photoconductive recording materials exist in differentconfigurations with one or more "active" layers coated on a conductingsubstrate and include optionally an outermost protective layer. By"active" layer is meant a layer that plays a role in the formation ofthe electrostatic charge image. Such a layer may be the layerresponsible for charge carrier generation, charge carrier transport orboth. Such layers may have a homogeneous structure or heterogeneousstructure.

Examples of active layers in said photoconductive recording materialhaving a homogeneous structure are layers made of vacuum-depositedphotoconductive selenium, doped silicon, selenium alloys and homogeneousphotoconducting polymer coatings, e.g. of poly(vinylcarbazole) orpolymeric binder(s) molecularly doped with an electron (negative chargecarrier) transporting compound or a hole (positive charge carrier)transporting compound such as particular hydrazones, amines andheteroaromatic compounds sensitized by a dissolved dye, so that in saidlayers both charge carrier generation and charge carrier transport takeplace.

Examples of active layers in said photoconductive recording materialhaving a heterogeneous structure are layers of one or morephotosensitive organic or inorganic charge generating pigment particlesdispersed in a polymer binder or polymer binder mixture in the presenceoptionally of (a) molecularly dispersed charge transport compound(s), sothat the recording layer may exhibit only charge carrier generationproperties or both charge carrier generation and charge transportproperties.

According to an embodiment that may offer photoconductive recordingmaterials with particularly low fatigue a charge generating and chargetransporting layer are combined in contiguous relationship. Layers whichserve only for the charge transport of charge generated in an adjacentcharge generating layer are e.g. plasma-deposited inorganic layers,photoconducting polymer layers, e.g. on the basis ofpoly(N-vinylcarbazole) or layers made of low molecular weight organiccompounds molecularly distributed in a polymer binder or binder mixture.

Useful charge carrier generating pigments (CGM's) belong to one of thefollowing classes:

a) perylimides, e.g. C.I. 71130 (C.I.=Colour Index) described in DBP 2237 539;

b) polynuclear quinones, e.g. anthanthrones such as C.I. 59 300described in DBP 2 237 678;

c) quinacridones, e.g. C.I. 46 500 described in DBP 2 237 679;

d) naphthalene 1,4,5,8-tetracarboxylic acid derived pigments includingthe perinones, e.g. Orange GR, C.I. 71 105 described in DBP 2 239 923;

e) tetrabenzoporphyrins and tetranaphthaloporphyrins, e.g. H₂-phthalocyanine in X-crystal form (X--H₂ Pc) described in U.S. Pat. No.3,357,989, metal phthalocyanines, e.g. CuPc C.I. 74 160 described in DBP2 239 924, indium phthalocyanine described in U.S. Pat. No. 4,713,312and tetrabenzoporphyrins described in EP 428,214 A; andnaphthalocyanines having siloxy groups bonded to the central metalsilicon described in EP 243,205 A;

f) indigo- and thioindigo dyes, e.g. Pigment Red 88, C.I. 73 312described in DBP 2 237 680;

g) benzothioxanthene derivatives as described e.g. in DeutschesAuslegungsschrift (DAS) 2 355 075;

h) perylene 3,4,9,10-tetracarboxylic acid derived pigments includingcondensation products with o-diamines as described e.g. in DAS 2 314051;

i) polyazo-pigments including bisazo-, trisazo- andtetrakisazo-pigments, e.g. Chlordiane Blue C.I. 21 180 described in DAS2 635 887, trisazo-pigments, e.g. as described in U.S. Pat. No.4,990,421 and bisazo-pigments as described in DeutschesOffenlegungsschrift (DOS) 2 919 791, DOS 3 026 653 and DOS 3 032 117;

j) squarylium dyes as described e.g. in DAS 2 401 220;

k) polymethine dyes;

l) dyes containing quinazoline groups, e.g. as described in GB-P1,416,602 according to the following general formula: ##STR1## in whichR and R¹ are either identical or different and denote hydrogen, C₁ -C₄alkyl, alkoxy, halogen, nitro or hydroxyl or together denote a fusedaromatic ring system;

m) triarylmethane dyes; and

n) dyes containing 1,5-diamino-anthraquinone groups,

o) inorganic photoconducting pigments e.g. Se, Se alloys, As₂ Se₃, TiO₂,ZnO, CdS, etc.

Organic charge carrier transporting substances may be either polymericor non-polymeric materials.

Examples of preferred polymeric positive hole charge carriertransporting substances are poly(N-vinylcarbazole), N-vinylcarbazolecopolymers, polyvinyl anthracene and the condensation products of analdehyde with two or more 1,2-dihydroquinoline molecules as described inU.S. Pat. No. 5,043,238.

Preferred non-polymeric materials for positive charge transport are:

a) hydrazones e.g. a p-diethylaminobenzaldehyde diphenyl hydrazone asdescribed in U.S. Pat. No. 4,150,987; and other hydrazones described inU.S. Pat. No. 4,423,129; U.S. Pat. No. 4,278,747, U.S. Pat. No.4,365,014, EP 448,843 A and EP 452,569 A, e.g. T191 from Takasago##STR2## b) aromatic amines e.g. N,N'-diphenyl, N,N-bis-m-tolylbenzidine as described in U.S. Pat. No. 4,265,990, tris(p-tolyl)amine asdescribed in U.S. Pat. No. 3,189,730: ##STR3##1,3,5-tris(aminophenyl)benzenes as described in U.S. Pat. No. 4,923,774;3,5-diarylaniline derivatives as described in EP 534,514 A, andtriphenyloxazole derivatives as described in EP 534,005 A;

c) heteroaromatic compounds e.g. N-(p-aminophenyl) carbazoles asdescribed in U.S. Pat. No. 3,912,509 and dihydroquinoline compounds asdescribed in U.S. Pat. No. 3,832,171, U.S. Pat. No. 3,830,647, U.S. Pat.No. 4,943,502, U.S. Pat. No. 5,043,238, EP 452,569 A and EP 462,327 Ae.g. ##STR4## d) triphenylmethane derivatives as described for examplein U.S. Pat. No. 4,265,990;

e) pyrazoline derivatives as described for example in U.S. Pat. No.3,837,851;

f) stilbene derivatives as described for example in Japanese Laid OpenPatent Application (JL-OP) 198,043/83.

The choice of binder for the charge generating layer (CGL) for a givencharge generating pigment (CGM) and a given charge transport layer (CTL)has a strong influence on the electro-optical properties of thephotoreceptors. One or more of the following phenomena can have anegative influence on the electro-optical properties of thephotoconductive recording material:

i) interfacial mixing between the CGL and the CTL resulting inCGM-doping of the CTL and CTM-doping of the CGL causing charge trapping;

ii) charge trapping in the CGL;

iii) poor charge transport in the CGL;

iv) poor charge transport blocking properties in the absence of ablocking layer.

Interfacial mixing between the CGL and the CTL can be avoided by using aCGL-binder or binders, which is/are insoluble in the solvent used fordissolving the CTL-binders in which CTM's exhibit optimum chargetransport properties. Limited is the range of solvents in whichefficient CTM's are soluble. The range of solvents in which bothCTL-binders and CTM's are soluble is extremely narrow and often limitedto chlorohydrocarbons such as methylene chloride. Methylene chloride isan extremely powerful solvent and the range of CGL-binders which istotally insoluble in methylene chloride is extremely limited, unless theCGL-binder is crosslinked in a subsequent hardening process.

Hardening is to be considered here as a treatment which renders thebinder of a charge generating layer of the photoconductive recordingmaterial insoluble in methylene chloride.

3. SUMMARY OF THE INVENTION

It is an object of the present invention to provide a multiple layerphoto-conductive recording material with improved photosensitivity.

It is still a further object of the present invention to provide aphotoconductive recording material wherein interfacial mixing of thecharge transporting layer with the charge generating layer is avoidedduring overcoating of the charge generating layer with a solution of thecharge transporting layer composition.

It is still a further object of the present invention to provide a saidphotoconductive recording material wherein the binder system for thecharge generating layer allows efficient charge transport in the chargegenerating layer and efficient charge injection into the chargetransporting layer which is a negative charge transporting layer.

In accordance with the present invention a photoconductive recordingmaterial is provided containing a support and a charge generating layer(CGL) in contiguous relationship (contact) with a charge transportinglayer (CTL), containing a p-charge transporting material (p-CTM),wherein the binder of said charge generating layer (CGL) is madeinsoluble in methylene chloride by crosslinking, and said binder iscomposed essentially of one or more polyepoxy compounds self-crosslinked(by self-condensation) under the influence of an amine catalyst and/orcrosslinked by reaction with at least one primary and/or secondary polyNH-group amine.

4. DETAILED DESCRIPTION OF THE INVENTION

The amino groups in said amines can be blocked temporarily to form astable coating composition wherefrom the amino groups are set free insitu in the coated layer. The blocking of the amino groups may proceedby transforming them into ketimine groups by reaction with a ketone,that is set free again by reaction with moisture (H₂ O) [ref. the book"The Chemistry of Organic Film Formers" by D. H. Solomon, John Wiley &Sons, Inc. New York (1967), the chapter "Epoxy Resins", p. 190-191].

The self-condensation of epoxy resins under the action of basiccatalysts such as monofunctional amines is described in said book onpages 186-188. Most epoxy resins are difunctional (or nearly so) interms of epoxy groups, whereby a crosslinked structure forms withprimary and/or secondary poly NH-group amines, e.g. ethylene diamine.

According to one embodiment a photoconductive recording materialaccording to the present invention has a charge generating layercontaining as the sole binder a crosslinked polymeric structure obtainedthrough self-condensation of polyepoxy compounds in the presence of acatalytic amount of amine or through the reaction of polyepoxycompounds, e.g. epoxy resins, with one or more primary and/or secondarypoly NH-group amines.

According to another embodiment a photoconductive recording materialaccording to the present invention has a charge generating layercontaining one or more polyepoxy compounds, optionally epoxy resins,self-crosslinked in the presence of one or more catalytically actingamines wherein the concentration of said amines is between 2 and 15% byweight of the total weight of said polyepoxy compounds and amines.

According to a further embodiment a photoconductive recording materialaccording to the present invention has a charge generating layercontaining a binder having said polymeric structure derived from one ormore polyepoxy compounds crosslinked with one or more of said polyNH-group amines wherein the equivalent ratio of the totality of epoxygroups and NH present in said polyamines is between 2.0:1 and 1:2.0.

According to a still further embodiment a photoconductive recordingmaterial according to the present invention has a charge generatinglayer containing a binder having said polymeric structure and at least30 wt % of charge generating material(s).

Examples of polyepoxy compounds suitable for use according to thepresent invention are: ##STR5## wherein R" is an alkyl group and a≧0##STR6## in which: X represents S, SO₂, ##STR7## each of R¹, R², R³, R⁴,R⁷ and R⁸ (same or different) represents hydrogen, halogen, an alkylgroup or an aryl group; each of R⁵ and R⁶ (same or different) representshydrogen, an alkyl group, an aryl group or together represent thenecessary atoms to close a cycloaliphatic ring, e.g. a cyclohexane ring;and x is zero or an integer. ##STR8## wherein R⁹ is an alkyl group;##STR9## wherein X has the same meaning as above; ##STR10## wherein eachof R¹⁰ and R¹¹ (same or different) represents hydrogen or an alkyl groupand b≧0.

Commercially available bisphenol A-epichlorhydrin epoxy resins accordingto formula II are:

EPON 828

EPON 1001

EPON 1002

EPON 1004

EPON 1007

EPON 1009

from Shell Chemical Co.

DER 331

DER 667

DER 668

DER 669

from Dow Chemical; and from Ciba-Geigy Switzerland:

ARALDITE GT 6071

ARALDITE GT 7203

ARALDITE GT 7097

ARALDITE GT 6099

A commercially available mixed bisphenol A/bisphenol F-epichlorhydrinepoxyresin according to formula II is:

EPON 235 from Shell Chemical Co.

A commercially available bisphenol F-epichlorhydrin epoxy resinaccording to formula II is:

ARALDITE GY 281 from Ciba-Geigy.

A commercially available epoxy resin according to formula IV is:

ARALDITE MY 721 from Ciba-Geigy.

Commercially available phenol novolak epoxy resins according to formulaV are:

DEN 431

DEN 438

DEN 439

from Dow Chemical; and from Ciba -Geigy:

ARALDITE GY 1180

ARALDITE EPN 1138

Examples of amines for use according to this invention, which are ableto render epoxy resins insoluble in methylene chloride by catalyzing theself-crosslinking of epoxy resins are cyclic aliphatic amines andtertiary amines, e.g.

piperidine

2,5-dimethylpiperazine

triethylamine

benzyldimethylamine (BDA)

2-dimethylaminomethylphenol (DMAMP) ##STR11##

Examples of poly NH-group amines for use according to this invention,which are able to render epoxy resins insoluble in methylene chlorideare:

i) aromatic poly NH-group amines or derivatives thereof e.g.

4,4'-diaminodiphenylmethane (DDM)-derivatives commercially available asEPICURE 153 from Shell Chemical and ARALDITE HY 830 from Ciba-Geigy;

4,4'-diaminodiphenylsulphone;

1,3,5-tris(4'-aminophenyl)benzene

meta-phenylenediamine ##STR12## ii) poly NH-group amines whereinaliphatic amino groups are attached to an aromatic backbone e.g.:

meta-xylylene diamine commercially available as EPILINK MX from Akzo,The Netherlands;

3-phenyl-2-propylamine

iii) cycloaliphatic poly NH-group amines e.g. isophorondiaminederivatives commercially available as EPILINK 420 from Akzo, TheNetherlands;

iv) heterocyclic poly NH-group amines e.g.

4-aminomethylpiperidine ##STR13##

The hardened polymeric binder structure obtained by self-condensation ofpolyepoxy compounds in the presence of catalytic amounts of amines orobtained by crosslinking reaction of polyepoxy compounds with primaryand/or secondary poly NH-group amines may be used in combination with atleast one other polymer serving as binding agent, e.g. in combinationwith acrylate and methacrylate resins, copolyesters of a diol, e.g.glycol, with isophthalic and/or terephthalic acid, polyacetals,polyurethanes, polyester-urethanes, aromatic polycarbonates, wherein apreferred combination contains at least 50% by weight of said hardenedpolymeric structure in the total binder content.

A polyester resin particularly suited for used in combination with saidhardened resins is DYNAPOL L 206 (registered trade mark of Dynamit Nobelfor a copolyester of terephthalic acid and isophthalic acid withethylene glycol and neopentyl glycol, the molar ratio of tere- toisophthalic acid being 3/2). Said polyester resin improves the adherenceto aluminium that may form a conductive coating on the support of therecording material.

Aromatic polycarbonates that are suitable for use in admixture with saidpolyepoxy compounds hardened with said amines can be prepared by methodssuch as those described by D. Freitag, U. Grigo, P. R. Muller and W.Nouvertne in the Encyclopedia of Polymer Science and Engineering, 2nded., Vol. II, pages 648-718, (1988) published by Wiley and Sons Inc.,and have one or more repeating units within the scope of followinggeneral formula: ##STR14## wherein: X, R¹, R², R³ and R⁴ have the samemeaning as described in general formula (II) above.

Aromatic polycarbonates having a molecular weight in the range of 10,000to 200,000 are preferred. Suitable polycarbonates having such a highmolecular weight are sold under the registered trade mark MAKROLON ofBayer AG, W-Germany.

MAKROLON CD 2000 (registered trademark) is a bisphenol A polycarbonatewith molecular weight in the range of 12,000 to 25,000 wherein R¹ =R²=R³ =R⁴ =H, X is ##STR15## with R⁵ =R⁶ =CH₃.

MAKROLON 5700 (registered trade mark) is a bisphenol A polycarbonatewith molecular weight in the range of 50,000 to 120,000 wherein R¹ =R²=R³ =R⁴ =H, X is ##STR16## with R⁵ =R⁶ =CH₃.

Bisphenol Z polycarbonate is an aromatic polycarbonate containingrecurring units wherein R¹ =R² =R³ =R⁴ =H, X is ##STR17## and R⁵together with R⁶ represents the necessary atoms to close a cyclohexanering.

Suitable electronically inactive binder resins for use in active layersof the present photoconductive recording material not containing saidpolyepoxy compounds hardened with said amines are e.g. the abovementioned polyester and polycarbonates, but also cellulose esters,acrylate and methacrylate resins, e.g. cyanoacrylate resins, polyvinylchloride, copolymers of vinyl chloride, e.g. copolyvinylchloride/acetate and copolyvinyl chloride/maleic anhydride.

Further useful binder resins for an active layer are silicone resins,polystyrene and copolymers of styrene and maleic anhydride andcopolymers of butadiene and styrene.

Charge transport layers in the photoconductors of the present inventionpreferably have a thickness in the range of 5 to 50 μm, more preferablyin range of 5 to 30 μm. If these layers contain low molecular weightcharge transport molecules, such compounds will preferably be present inconcentrations of 30 to 70% by weight.

The presence of one or more spectral sensitizing agents can have anadvantageous effect on the charge transport. In that connectionreference is made to the methine dyes and xanthene dyes described inU.S. Pat. No. 3,832,171. Preferably these dyes are used in an amount notsubstantially reducing the transparency in the visible light region(420-750 nm) of the charge transporting layer so that the chargegenerating layer still can receive a substantial amount of the exposurelight when exposed through the charge transporting layer.

The charge transporting layer may contain compounds substituted withelectron-acceptor groups forming an intermolecular charge transfercomplex, i.e. donor-acceptor complex when electron donor chargetransport compounds are present. Useful compounds havingelectron-accepting groups are nitrocellulose and aromaticnitro-compounds such as nitrated fluorenone-9 derivatives, nitrated9-dicyanomethylene fluorenone derivatives, nitrated naphthalenes andnitrated naphthalic acid anhydrides or imide derivatives. The preferredconcentration range of said compounds having electron acceptor groups issuch that the donor/acceptor weight ratio is 2.5:1 to 1,000:1.

Compounds acting as stabilising agents against deterioration byultra-violet radiation, so-called UV-stabilizers, may also beincorporated in said charge transport layer. Examples of UV-stabilizersare benztriazoles.

For controlling the viscosity and aiding deaeration of the coatingcompositions and controlling their optical clarity silicone oils may beadded to the charge transport layer.

As charge generating compounds for use in a recording material accordingto the present invention any of the organic pigments belonging to one ofthe following classes and able to transfer electrons to electrontransporting materials may be used:

a) perylimides, e.g. C.I. 71 130 (C.I.=Colour Index) described in DBP 2237 539,

b) polynuclear quinones, e.g. anthanthrones such as C.I. 59 300described in DBP 2 237 678,

c) quinacridones, e.g. C.I. 46 500 described in DBP 2 237 679,

d) naphthalene 1,4,5,8-tetracarboxylic acid derived pigments includingthe perinones, e.g. Orange GR, C.I. 71 105 described in DBP 2 239 923,

e) tetrabenzoporphyrins and tetranaphthaloporphyrins, e.g. H₂-phthalocyanine in X-crystal form (X--H₂ Pc) described in U.S. Pat. No.3,357,989, metal phthalocyanines, e.g. CuPc C.I. 74 160 described in DBP2 239 924, indium phthalocyanine described in U.S. Pat. No. 4,713,312,tetrabenzoporphyrins described in EP 428 214 A, siliconnaphthalocyanines having siloxy groups bonded to the central silicon asdescribed in EP-A 0243 205 and X- and β-morphology H₂ Pc(CN)_(x), H₂Pc(CH₃)_(x) and H₂ PcCl_(x) pigments.

f) indigo- and thioindigo dyes, e.g. Pigment Red 88, C.I. 73 312described in DBP 2 237 680,

g) benzothioxanthene-derivatives as described e.g. in DAS 2 355 075,

h) perylene 3,4,9,10-tetracarboxylic acid derived pigments includingcondensation products with o-diamines as described e.g. in DAS 2 314051,

i) polyazo-pigments including bisazo-, trisazo- andtetrakisazo-pigments, e.g. Chlordiane Blue C.I. 21 180 described in DAS2 635 887, and bisazopigments described in DOS 2 919 791, DOS 3 026 653and DOS 3 032 117,

j) squarilium dyes as described e.g. in DAS 2 401 220,

k) polymethine dyes.

l) dyes containing quinazoline groups, e.g. as described in GB-P 1 416602 according to the following general formula: ##STR18## wherein R' andR" have the meaning described in said GB-P document.

Inorganic substances suited for photogenerating negative charges in arecording material according to the present invention are e.g. amorphousselenium and selenium alloys e.g. selenium-tellurium,selenium-tellurium-arsenic and selenium-arsenic and inorganicphotoconductive crystalline compounds such as cadmium sulphoselenide,cadmiumselenide, cadmium sulphide and mixtures thereof as disclosed inU.S. Pat. No. 4,140,529.

The thickness of the charge generating layer is preferably not more than10 μm, more preferably not more than 5 μm.

In the recording materials of the present invention an adhesive layer orbarrier layer may be present between the charge generating layer and thesupport or the charge transport layer and the support. Useful for thatpurpose are e.g. a polyamide layer, nitrocellulose layer, hydrolysedsilane layer, or aluminium oxide layer acting as blocking layerpreventing positive or negative charge injection from the support side.The thickness of said barrier layer is preferably not more than 1micron.

The conductive support may be made of any suitable conductive material.Typical conductors include aluminum, steel, brass and paper and resinmaterials incorporating or coated with conductivity enhancingsubstances, e.g. vacuum-deposited metal, dispersed carbon black,graphite and conductive monomeric salts or a conductive polymer, e.g. apolymer containing quaternized nitrogen atoms as in Calgon Conductivepolymer 261 (trade mark of Calgon Corporation, Inc., Pittsburgh, Pa.,U.S.A.) described in U.S. Pat. No. 3,832,171.

According to a particular embodiment the support is an insulating resinsupport provided with an aluminium layer forming a conducting coating.

The support may be in the form of a foil, web or be part of a drum.

An electrophotographic recording process according to the presentinvention comprises the steps of:

(1) overall electrostatically charging, e.g. with corona-device, thephotoconductive layer containing at least one polyepoxy compoundhardened with at least one of said amines;

(2) image-wise photo-exposing said layer thereby obtaining a latentelectrostatic image, that may be toner-developed.

When applying a bilayer-system electrophotographic recording materialincluding on an electrically conductive support a photosensitive chargegenerating layer that contains one or more polyepoxy compounds hardenedwith one or more of said amines in contiguous relationship with a chargetransporting layer, the photo-exposure of the charge generating layerproceeds preferably through the charge transporting layer but may bedirect if the charge generating layer is uppermost or may proceedlikewise through the conductive support if the latter is transparentenough to the exposure light.

The development of the latent electrostatic image commonly occurspreferably with finely divided electrostatically attractable material,called toner particles that are attracted by coulomb force to theelectrostatic charge pattern. The toner development is a dry or liquidtoner development known to those skilled in the art.

In positive-positive development toner particles deposit on those areasof the charge carrying surface which are in positive-positive relationto the original image. In reversal development, toner particles migrateand deposit on the recording surface areas which are innegative-positive image value relation to the original. In the lattercase the areas discharged by photo-exposure obtain by induction througha properly biased developing electrode a charge of opposite charge signwith respect to the charge sign of the toner particles so that the tonerbecomes deposited in the photo-exposed areas that were discharged in theimagewise exposure (ref.: R. M. Schaffert "Electrophotography"--TheFocal Press--London, N.Y., enlarged and revised edition 1975, p. 50-51and T. P. Maclean "Electronic Imaging" Academic Press--London, 1979, p.231).

According to a particular embodiment electrostatic charging, e.g. bycorona, and the imagewise photo-exposure proceed simultaneously.

Residual charge after toner development may be dissipated beforestarting a next copying cycle by overall exposure and/or alternatingcurrent corona treatment.

Recording materials according to the present invention depending on thespectral sensitivity of the charge generating layer may be used incombination with all kinds of photon-radiation, e.g. light of thevisible spectrum, infra-red light, near ultra-violet light and likewiseX-rays when electron-positive hole pairs can be formed by said radiationin the charge generating layer. Thus, they can be used in combinationwith incandescent lamps, fluorescent lamps, laser light sources or lightemitting diodes by proper choice of the spectral sensitivity of thecharge generating substance or mixtures thereof.

The toner image obtained may be fixed onto the recording material or maybe transferred to a receptor material to form thereon after fixing thefinal visible image.

A recording material according to the present invention showing aparticularly low fatigue effect can be used in recording apparatusoperating with rapidly following copying cycles including the sequentialsteps of overall charging, imagewise exposing, toner development andtoner transfer to a receptor element.

The following examples further illustrate the present invention. Allparts, ratios and percentages are by weight unless otherwise stated.

The evaluations of electrophotographic properties determined on therecording materials of the following examples relate to the performanceof the recording materials in an electrophotographic process with areusable photoreceptor. The measurements of the performancecharacteristics were carried out by using a sensitometric measurement inwhich the discharge was obtained for 16 different exposures in additionto zero exposure. The photoconductive recording sheet material wasmounted with its conductive backing on an aluminium drum which wasearthed and rotated at a circumferential speed of 10 cm/s. The recordingmaterial was sequentially charged with a positive corona at a voltage of-5.7 kV operating with a grid voltage of -600 V. Subsequently therecording material was exposed (simulating image-wise exposure) with alight dose of monochromatic light obtained from a monochromatorpositioned at the circumference of the drum at an angle of 45° withrespect to the corona source. The photo-exposure lasted 200 ms.Thereupon, the exposed recording material passed an electrometer probepositioned at an angle of 180° with respect to the corona source. Aftereffecting an overall post-exposure with a halogen lamp producing 355mJ/m2 positioned at an angle of 270° with respect to the corona source anew copying cycle started. Each measurement relates to 80 copying cyclesin which the photoconductor is exposed to the full light sourceintensity for the first 5 cycles, then sequentially to the light sourcethe light output of which is moderated by grey filters of opticaldensities 0.2, 0.38, 0.55, 0.73, 0.92, 1.02, 1.20, 1.45, 1.56, 1.70,1.95, 2.16, 2.25, 2.51 and 3.21, each for 5 cycles and finally to zerolight intensity for the last 5 cycles.

The electro-optical results quoted in the EXAMPLES 1 to 20 hereinafterrefer to charging level at zero light intensity (CL) and to discharge ata light intensity corresponding to the light source intensity moderatedby a grey filter to the exposure indicated to a residual potential RP.

The % discharge is: ##EQU1##

For a given corona voltage, corona current, separating distance of thecorona wires to recording surface and drum circumferential speed thecharging level CL is only dependent upon the thickness of the chargetransport layer and its specific resistivity. In practice CL expressedin volts should be preferably ≧30 d, where d is the thickness in μm ofthe charge transport layer.

The structures of the CTM's used in the examples (P1 to P6) are givenbelow: ##STR19##

All ratios and percentages mentioned in the Examples are by weight.

EXAMPLE 1

In the production of a composite layer electrophotographic recordingmaterial a 175 μm thick polyester film pre-coated with avacuum-deposited layer of aluminium was doctor-blade coated with adispersion of charge generating pigment to a thickness of 0.9 μm.

Said dispersion was prepared by mixing for 40 hours in a ball mill 2 gof metal free X-phthalocyanine (FASTOGEN BLUE 8120B from Dainippon Inkand Chemicals Inc.); 0.27 g of ARALDITE GT7203 (tradename for abisphenol A-epichlorhydrin epoxy resin from Ciba-Geigy); 9.66 g ofbutan-2-one and 16.44 g of methylene chloride. 1.56 g of ARALDITE T7203(tradename), 5.3 g of butan-2-one, 8.952 g of methylene chloride and0.168 g of 2.5 dimethylpiperazine (a catalytically active heterocyclicamine) were then added to the dispersion and the dispersion mixed for afurther 15 minutes.

The applied layer was dried and thermally hardened for 18 hours at 150°C. and then overcoated using a doctor-blade coater with a filteredsolution consisting of 3 g of the CTM P1; 3 g of MAKROLON 5700(tradename for a bisphenol A polycarbonate from Bayer A.G).; and 44 g ofmethylene chloride to a thickness in dry state of 12.1 μm. Dryingproceeded at 50° C. for 16 hours.

The electro-optical characteristics of the thus obtained photoconductiverecording materials were determined as described above. At a charginglevel of -547 V and an exposure dose of 660 nm light (I₆₆₀ t) of 10mJ/m², the following results were obtained:

    ______________________________________                                        CL =                  -547 V                                                  RP =                  -110 V                                                  % Discharge =         79.9                                                    ______________________________________                                    

EXAMPLES 2 AND 3

The photoconductive recording materials of examples 2 and 3 wereproduced as described for example 1 except that alternativecatalytically active amines were used in the materials of examples 2 and3 and hardening conditions of 12 hours at 150° C. and 1 hour at 100° C.were used respectively. The weight percentages of the ARALDITE GT7203(tradename) and catalytically active amine in the CGL's calculated onthe basis of the solids content of the hardener are given in Table 1together with the CTL layer thicknesses (d_(CTL)).

The electro-optical characteristics of the thus obtained photoconductiverecording materials were determined as described above and the resultssummarized in Table 1 together with these for the photoconductiverecording material of example 1.

                                      TABLE 1                                     __________________________________________________________________________    ARALDITE                                                                      GT7203              Hardener                                                                           I.sub.660 t = 10 mJ/m.sup.2                          Example                                                                            conc.  Catalytically                                                                         conc.                                                                              d.sub.CTL                                                                        CL  RP  % Dis-                                    No.  [wt %] active amine                                                                          [wt %]                                                                             [μm]                                                                          [V] [V] charge                                    __________________________________________________________________________    1    45.8   2,5-dimethyl-                                                                         4.2  12.1                                                                             -547                                                                              -110                                                                              79.9                                                  piperazine                                                        2    47     piperidine                                                                            3    14.1                                                                             -538                                                                              -150                                                                              72.1                                      3    47     2,4,6-tris(di-                                                                        3    15.1                                                                             -621                                                                              -232                                                                              62.6                                                  methylamino-                                                                  methyl)-phenol                                                    __________________________________________________________________________

EXAMPLES 4 TO 12

The photoconductive recording materials of examples 4 to 12 wereproduced as described for example 1 except that different aromatic polyNH-group amine hardeners and different hardening conditions were used asindicated in Table 2. The amounts of ARALDITE GT7203 (tradename) andhardener were adjusted to obtain a theoretical degree of hardening of100%. The weight percentages of the ARALDITE GT7203 (tradename) andhardener in the CGL's calculated on the basis of the solids content ofthe hardener are given in Table 2 together with the CTL layerthicknesses (d_(CTL)).

The electro-optical characteristics of the thus obtained photoconductiverecording materials were determined as described above and the resultssummarized in Table 2.

                                      TABLE 2                                     __________________________________________________________________________                          Hard-                                                       ARALDITE      Hard-                                                                             ening                                                   Exam-                                                                             GT 7203       ener                                                                              condit.                                                                              I.sub.660 t = 10 mJ/m.sup.2                      ple conc.         conc.                                                                             Temp.                                                                             Time                                                                             d.sub.CTL                                                                         CL  RP  % dis-                               no. [wt %] Hardener                                                                             [wt %]                                                                            (°C.)                                                                      (hrs)                                                                            [μm]                                                                           [V] [V] charge                               __________________________________________________________________________    4   46.3   4,4'-diamino-                                                                        3.7 100 2  10.1                                                                              -550                                                                              -128                                                                              76.7                                            diphenyl-                                                                     methane                                                            5   42.23  ARALDITE                                                                             7.77                                                                              100 2  12.1                                                                              -543                                                                              -124                                                                              77.2                                            HY830*                                                             6   45.48  4,4'-diamino-                                                                        4.52                                                                              100 24 13.1                                                                              -540                                                                              -113                                                                              79.1                                            diphenyl-                                                                     sulfone                                                            7   45.71  AP1    4.29                                                                              100 2  10.1                                                                              -519                                                                              -112                                                                              78.4                                 8   41.8   AP2    8.2 100 2  12.1                                                                              -570                                                                              -122                                                                              78.6                                 9   41.46  AP3    8.54                                                                              100 2  11.1                                                                              -567                                                                              -120                                                                              78.8                                 10  38.52  AP4    11.48                                                                             100 2  12.1                                                                              -586                                                                              -157                                                                              73.2                                 11  41.43  AP5    8.57                                                                              100 2  15.1                                                                              -551                                                                              -101                                                                              81.7                                 12  47.92  meta-pheny-                                                                          2.08                                                                              150 18 14.1                                                                              -561                                                                              -121                                                                              78.4                                            lene-                                                                         diamine                                                            __________________________________________________________________________     *tradename of CibaGeigy.                                                 

EXAMPLES 13 AND 14

The photoconductive recording materials of examples 13 and 14 wereproduced as described for example 7 except that different epoxy resinswere used (as indicated in Table 3) instead of ARALDITE GT7203(tradename). The amounts of epoxy resin and hardener were adjusted toobtain a theoretical degree of hardening of 100%. The weight percentagesof the epoxy resin and hardener in the CGL's calculated on the basis ofthe solids content of the hardener are given in Table 3 together withthe CTL layer thicknesses (d_(CTL)).

The electro-optical characteristics of the thus obtained photoconductiverecording materials were determined as described above and the resultsare summarized in Table 3 together with those for the photoconductiverecording material of example 7.

                                      TABLE 3                                     __________________________________________________________________________                    Epoxy                                                                         resin                                                                             AP1 I.sub.660 t = 10 mJ/m.sup.2                           Example                                                                            Epoxy resin                                                                              conc.                                                                             conc.                                                                             d.sub.CTL                                                                        CL  RP  % dis-                                     no.  (trade name)                                                                             [wt %]                                                                            [wt %]                                                                            [μm]                                                                          [V] [V] charge                                     __________________________________________________________________________     7   ARALDITE GT7203                                                                          45.71                                                                             4.29                                                                              10.1                                                                             -519                                                                              -112                                                                              78.4                                       13   ARALDITE GY281                                                                           36.9                                                                              13.1                                                                              13.1                                                                             -576                                                                              -152                                                                              73.6                                       14   DEN 438    37.64                                                                             12.36                                                                             14.1                                                                             -559                                                                              -120                                                                              78.5                                       __________________________________________________________________________

EXAMPLES 15 AND 16

The photoconductive recording materials of examples 15 and 16 wereproduced as described for example 1 except that different poly NH-groupamines wherein aliphatic amino groups are attached to an aromaticbackbone were used as hardeners instead of 2,5-dimethylpiperazine andthey were hardened as indicated in Table 4. The amounts of ARALDITEGT7203 (tradename) and poly NH-group amine were adjusted to obtain atheoretical degree of hardening of 100%. The weight percentages ofARALDITE GT7203 (tradename) and poly NH-group amine calculated on thebasis of the solids content of the reactants are given in Table 4together with the CTL layer thicknesses.

The electro-optical characteristics of the thus obtained photoconductiverecording materials were determined as described above and the resultsare summarized in Table 4.

                                      TABLE 4                                     __________________________________________________________________________                           Hard-                                                      ARALDITE       Hard-                                                                             ening                                                  Exam-                                                                             GT 7203        ener                                                                              conditions                                                                           I.sub.660 t = 10 mJ/m.sup.2                     ple conc.          conc.                                                                             Temp.                                                                             Time                                                                             d.sub.CTL                                                                        CL  RP  % dis-                               no. [wt %] Hardener                                                                              [wt %]                                                                            (°C.)                                                                      (hrs)                                                                            [μm]                                                                          [V] [V] charge                               __________________________________________________________________________    15  47.07  EPILINK MX*                                                                           2.93                                                                              150 16 13.1                                                                             -541                                                                              -112                                                                              79.3                                 16  45.1   3-phenyl-2-                                                                           4.9 150 18 14.1                                                                             -561                                                                               -98                                                                              82.5                                            propylamine                                                        __________________________________________________________________________     *tradename of Akzo, The Netherlands.                                     

EXAMPLES 17 AND 18

The photoconductive recording materials of examples 17 and 18 wereproduced as described for example 1 except that cycloaliphatic polyNH-group amines were used as hardeners and hardening took place underthe conditions indicated in Table 5. The amounts of ARALDITE GT7203(tradename) and poly NH-group amine were adjusted to obtain atheoretical degree of hardening of 100%. The weight percentages of theARALDITE GT7203 (tradename) and poly NH-group amine in the CGL'scalculated on the basis of the solids content of the reactants are givenin Table 5 together with the CTL layer thicknesses (d_(CTL)).

The electro-optical characteristics of the thus obtained photoconductiverecording materials were determined as described above and the resultsare summarized in Table 5.

                                      TABLE 5                                     __________________________________________________________________________                           Hard-                                                      ARALDITE       Hard-                                                                             ening                                                  Exam-                                                                             GT 7203                                                                              Poly NH-group                                                                         ener                                                                              condit.                                                                              I.sub.660 t = 10 mJ/m.sup.2                     ple conc.  amine   conc.                                                                             Temp.                                                                             Time                                                                             d.sub.CTL                                                                        CL  RP  % dis-                               no. [wt %] hardener                                                                              [wt %]                                                                            (°C.)                                                                      (hrs)                                                                            [μm]                                                                          [V] [V] charge                               __________________________________________________________________________    17  40.04  EPILINK 420*                                                                          9.96                                                                              150 16  7.1                                                                             -411                                                                               -87                                                                              78.8                                 18  46.81  Isophoron-                                                                            3.19                                                                              100  2 13.1                                                                             -589                                                                              -151                                                                              73.9                                            diamine                                                            __________________________________________________________________________     *trademark of Akzo, The Netherlands.                                     

EXAMPLES 19 AND 20

The photoconductive recording materials of examples 19 and 20 wereproduced as described in example 1 except that heterocyclic polyNH-group amines were used as hardeners instead of 2,5-dimethylpiperazineand hardening took place under the conditions indicated in Table 6. Theamounts of ARALDITE GT7203 (tradename) and poly NH-group amine wereadjusted to obtain a theoretical degree of hardening at 100%. The weightpercentages of ARALDITE GT7203 (tradename) and poly NH-group aminecalculated on the basis of the solids contents of the reactants aregiven in Table 6 together with the CTL layer thicknesses (d_(CTL)).

The electro-optical properties of the thus obtained photoconductiverecording materials were determined as described above and the resultsare summarized in Table 6.

                                      TABLE 6                                     __________________________________________________________________________                           Hard-                                                      ARALDITE       Hard-                                                                             ening                                                  Exam-                                                                             GT 7203                                                                              Poly NH-group                                                                         ener                                                                              condit.                                                                              I.sub.660 t = 10 mJ/m.sup.2                     ple conc.  amine   conc.                                                                             Temp.                                                                             Time                                                                             d.sub.CTL                                                                        CL  RP  % dis-                               no. [wt %] hardener                                                                              [wt %]                                                                            (°C.)                                                                      (hrs)                                                                            [μm]                                                                          [V] [V] charge                               __________________________________________________________________________    19  47.2   4-aminomethyl-                                                                        2.8 2   100                                                                              12.1                                                                             -567                                                                              -178                                                                              68.6                                            piperidine                                                         20  46.15  4-amino-                                                                              3.85                                                                              2   100                                                                              14.1                                                                             -592                                                                              -164                                                                              72.3                                            2,2,6,6-                                                                      tetramethyl-                                                                  piperidine                                                         __________________________________________________________________________

We claim:
 1. A photoconductive recording material containing a supportand a charge generating layer (CGL) in contiguous relationship with acharge transporting layer (CTL) containing a p-charge transportingmaterial (p-CTM), said charge generating layer (CGL) not containing acharge transporting material and comprising a charge generating materialand a binder, wherein said binder is made insoluble in methylenechloride by crosslinking and said binder is composed essentially of oneor more polyepoxy compounds self-crosslinked under the influence of anamine catalyst and/or crosslinked by reaction with at least one primaryand/or secondary poly NH-group amine.
 2. Photoconductive recordingmaterial according to claim 1, wherein said charge generating layer(CGL) contains as the sole binder a crosslinked polymeric structureobtained through self-condensation of polyepoxy compounds in thepresence of a catalytic amount of amine or through the reaction ofpolyepoxy compounds with one or more primary and/or secondary polyNH-group amines.
 3. Photoconductive recording material according toclaim 1, wherein said charge generating layer contains one or morepolyepoxy compounds self-crosslinked in the presence of one or morecatalytically acting amines wherein the concentration of said amines isbetween 2 and 15% by weight of the total weight of said polyepoxycompounds and amines.
 4. Photoconductive recording material according toclaim 1, wherein said charge generating layer contains a binder havingsaid polymeric structure derived from one or more polyepoxy compoundscrosslinked with one or more of said polyamines wherein the equivalentratio of the totality of epoxy groups and NH present in said polyNH-group amines is between 2.0:1 and 1:2.0.
 5. Photoconductive recordingmaterial according to claim 1, wherein said polyepoxy compounds servingas crosslinking agents are within the scope of at least one of thefollowing formulae (I), (II), (III), (IV) and (V): ##STR20## wherein R"is an alkyl group and a≧0 ##STR21## in which: X represents one of S,SO₂, ##STR22## each of R¹, R², R³, R⁴, R⁷ and R⁸ (same or different)represents one of hydrogen, halogen, an alkyl group or an aryl group;each of R⁵ and R⁶ (same or different) represents hydrogen, an alkylgroup, an aryl group or together represent one of the necessary atoms toclose a cycloaliphatic ring, andx is zero or an integer ##STR23##wherein R⁹ is an alkyl group; ##STR24## wherein X has the same meaningas above; ##STR25## wherein each of R¹⁰ and R¹¹ (same or different)represents hydrogen or an alkyl group and b≧0.
 6. Photoconductiverecording material according to claim 1, wherein the amino groups insaid amines have been blocked temporarily to form a stable coatingcomposition wherefrom the amino groups are set free in situ in thecoated layer.
 7. Photoconductive recording material according to claim1, wherein said polymeric reaction products obtained by crosslinkingsaid polyepoxy compounds with said amines are used in combination withat least one other polymer serving as binding agent.
 8. Photoconductiverecording material according to claim 7, wherein said other polymer isselected from the group consisting of an acrylate resin, methacrylateresin, copolyester of a diol with isophthalic and/or terephthalic acid,polyacetal, polyurethane, polyester-urethane and aromatic polycarbonate.9. Photoconductive recording material according to claim 7, wherein saidother polymer is present in said combination in an amount less than 50%by weight of the total binder content.
 10. Photoconductive recordingmaterial according to claim 1, wherein said support consists ofaluminium or is a support provided with an aluminium layer forming aconductive coating.